Achieving reliable networking for the generic autonomous platform for sensor systems : (GAP4S)
Abstract: Networks of wireless integrated sensors are often used to monitorparameters distributed in the environment. These parameters arerelated to a variety of applications such as security, patientmonitoring, chemical and biological hazard detection. Some solutionsrely on replaceable batteries with a limited life-time to providelong-term sensor operation. Others envision short transmission rangesensors (few meters) that harvest their energy from variousenvironmental sources (e.g., solar, vibrations, acoustic noise). TheGeneric Autonomous Platform for Sensors (GAP4S) project explores anapproach for wireless sensors that is complementary to these andother pre-existing solutions.In GAP4S, the wireless sensor micro-battery is remotely rechargedvia a microwave signal. Medium transmission ranges in the tens tohundreds of meters are possible. Within these wireless transmissionranges, a base-station collects data transmitted by the sensors andacts as the access point to a wider (typically wired) communicationnetwork, e.g., the Internet. The authorized user can, therefore,remotely connect to, monitor, and manage both the sensor network andthe individual sensors. An essential component of GAP4S is itsend-to-end network reliability solution, which ensures the deliveryof data generated at the sensor to the interested user across boththe wireless and wired segments.This dissertation investigates ways to achieve reliable networkingfor GAP4S over both the wireless and the wired segments. A speciallydesigned solution is provided in each segment.In the wireless segment, error-free transmissions from the sensornode to the base-station is achieved using automatic repeat request(ARQ) protocols at layer 2. Two classes of ARQ protocols aredesigned and compared. The first is the conventional ARQ, wherebythe data frame is retransmitted by the originating sensor untilsuccessfully received by the base-station. The second class takesadvantage of cooperative radio communications, wherebymultiple neighboring sensor nodes may combine their efforts duringthe retransmission process. The ARQ protocols are compared in termsof their saturation throughput, i.e., the maximum data flow that thesensor node can sustain constrained to the available energy amount.In a variety of scenarios --- current and future expected circuitenergy consumptions --- the cooperative ARQ protocols may more thandouble the saturation throughput when compared to conventional ARQprotocols. Equivalently, it can be said that the energy required tooperate the system may be reduced by half.In the wired segment, fault tolerant networking is achieved by meansof protection switching at layer 3. Given the increasinglywidespread use of Wavelength Division Multiplexed (WDM) backbonenetworks, the protection switching scheme is designed to operate inconjunction with WDM. Optical circuits are made reliable by means ofa Shared Path Protection (SPP) switching scheme. The SPP scheme isgeneralized to guarantee Differentiated levels of Reliability (DiR)to the user. In the SPP-DiR combined scheme the desired level ofreliability may be guaranteed while minimizing the required networkresources, i.e., wavelengths. This feature makes it possible tosupport more optical connections and users when compared to otherexisting protection switching schemes.
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